Powder Metallurgy Alloys Research Articles

Thermal Mechanical Processing of Press and Sinter Al-Cu-Mg-Sn-(AlN) Metal Matrix Composite Materials

The forging of sintered aluminum powder metallurgy alloys is currently viewed as a promising industrial technology for the manufacture of complex engineered products. The powder metallurgy process facilitates the use of admixed ceramic particles to produce aluminum metal matrix composites. However, fundamental data on the thermal-mechanical response of commercially relevant powder metallurgy alloy systems under varying conditions of temperature and strain rate are lacking. To address this constraint, the current study investigates the thermal-mechanical processing response of a family of metal matrix composite materials that employ a commercially exploited base alloy system coupled with admixed additions of aluminum nitride. Industrially-sintered compacts were tested under hot compression using a Gleeble 3500 thermal-mechanical test system to quantify their flow behavior. The nominal workability was assessed as a function of material formulation, sintered preform condition, and processing parameters (temperature and strain rate). Optical metallography and electron backscatter diffraction were used to observe the grain evolution through deformation. Full densification was achieved for materials with ceramic concentrations of 2% volume or less. Zener-Hollomon constituent analyses were also completed to elucidate a more comprehensive understanding the flow behavior inherent to each material. Flow behavior varied directly with the sintered density, which was influenced by the concentration and nature of ceramic particulate.

Fatigue crack growth characteristics for powder nickel based metallurgical superalloys at elevated temperatures

AbstractThis study presents experimental results regarding the fatigue crack growth characteristics of nickel‐based powder metallurgical superalloys used in aircraft turbine disks. The powder metallurgy alloys are manufactured using metal powders with a particulate diameter of less than 1 mm. The powder metallurgy alloys used in aircraft parts or turbine blades have excellent mechanical properties, fatigue resistance, oxidation resistance, and corrosion resistance at elevated temperatures. However, fatigue cracks arising from defects in the materials are unpredictable because they depend upon the manufacturing technique. As it is known that structural components may need to operate at elevated temperatures, the behavior of fatigue crack propagation at elevated temperatures is considered. The fatigue crack growth tests are conducted at typical operating conditions of stress ratios and elevated temperatures. Fatigue crack growth rate is measured using the direct current potential drop method, and evaluated by the Forman‐Mettu equation. Considering ΔKth as an important design variable, empirical constants were derived so that the analytic ΔKth value can be obtained directly at a given temperature. Fractography of the fractured specimens was performed using a scanning electron microscopy.

Effect of Phosphorus Addition on Dry Sliding Behavior of Fe–P Alloys Prepared by Powder Metallurgy

Iron–phosphorus powder metallurgy (P/M) alloys having 0, 0.35 and 0.65 wt.% P have been prepared by hot-forging technique. Hot forging consists of heating encapsulated powder at a temperature of 1050 °C in the atmosphere of hydrogen gas followed by hot forging. These hot-forged specimens have been subjected to dry sliding adhesive wear test at a normal load of 19.6, 29.4, and 39.2 N, at a constant sliding speed of 2.2 m/s and for a sliding distance of 4000 m using a pin-on-disk wear testing machine. Archard wear coefficient has been found to decrease from 2.5 × 10−7 to 1.4 × 10−7 with increasing phosphorus content in the alloys. The average coefficient of friction has also been found to decrease more or less linearly with increasing load as well as with increasing phosphorus content in the alloy. The mechanism of wear is primarily oxidative in nature, which has been confirmed by SEM–EDS analysis of the worn surfaces.

Influence of Hot Extrusion and Aging Treatment on the Properties of Biodegradable Mg-Zn-Y Alloy

Abstract Mg-6Zn-1Y (mass fraction, %) alloys were prepared for degradable biomaterials. The billets of the alloy were produced by powder metallurgy (PM) method and then hot extruded. The extruded samples were aged for 24 and 72 h at 150 °C. The microstructure and corrosion behavior of the experimental alloys were investigated. The microstructure observations indicate that the alloys contain α-Mg, MgZn, MgZn2 and Mg3YZn6 (I-phase) phases. The hot extrusion process significantly refines the grains and leads to better mechanical properties with the value of compressive strength in the range of 365∼399 MPa, and better corrosion resistance for the PM alloy shows higher hydrogen volume in the immersion test. Furthermore, due to more uniform corrosion behavior, the alloy aged for 72 h presents lower corrosion rate and corrosion current density in the immersion test and potentiodynamic polarization test, and higher resistance value (Rp) results from the electrochemical impedance spectroscopy (EIS), which means the alloy aged for 72 h exhibits better corrosion resistance than the other three alloys.

Comparison Study on Additive Manufacturing (AM) and Powder Metallurgy (PM) AlSi10Mg Alloys

The microstructural and mechanical properties of AlSi10Mg alloys fabricated by additive manufacturing (AM) and powder metallurgy (PM) routes were investigated and compared. The microstructures were examined by scanning electron microscopy assisted with electron-dispersive spectroscopy. The crystalline features were studied by x-ray diffraction and electron backscatter diffraction. Room-temperature tensile tests and Vickers hardness measurements were performed to characterize the mechanical properties. It was found that the AM alloy had coarser Al grains but much finer Si precipitates compared with the PM alloy. Consequently, the AM alloy showed more than 100% increment in strength and hardness compared with the PM alloy due to the presence of ultrafine forms of Si, while exhibiting moderate ductility.

Dry Sliding Wear of Fe Based Powder Processed Through Hot Powder Forging Technique

This research investigates the effect of normal load, alloy composition and hardness on the coefficient of friction and wear rate of Iron-Phosphorus Powder metallurgy (Fe-P P/M) alloys. The specimens were prepared from hot forged alloys (Fe-1.3wt.%P, Fe-2wt.%P and Fe-3wt.%P) were tested using Pin on disc apparatus. The wear rate increases as increasing in the normal loads. The coefficient of friction was inversely proportional to hardness. Since the phosphorus addition increases from 1.3 to 3 wt.% the volume percentage of phosphide (Fe3P) increased from 21 to 34vol.% which improves the hardness. The wear mechanism of the alloys is presented and discussed.

Effects of Post-Sinter Processing on an Al–Zn–Mg–Cu Powder Metallurgy Alloy

The objective of this work was to study the effects of several post-sinter processing operations (heat-treatment, sizing, shot peening) on a press-and-sinter 7xxx series aluminum powder metallurgy (PM) alloy. The characterization of the products was completed through a combination of non-contact surface profiling, hardness measurements, differential scanning calorimetry (DSC), transmission electron microscopy (TEM), X-ray diffraction (XRD), tensile, and three-point bend fatigue testing. It was determined that sizing in the as-quenched state imparted appreciable reductions in surface hardness (78 HRB) and fatigue strength (168 MPa) relative to counterpart specimens that were sized prior to solutionizing (85 HRB and 228 MPa). These declines in performance were ascribed to the annihilation of quenched in vacancies that subsequently altered the nature of precipitates within the finished product. The system responded well to shot peening, as this process increased fatigue strength to 294 MPa. However, thermal exposure at 353 K (80 °C) and 433 K (160 °C) then reduced fatigue performance to 260 MPa and 173 MPa, respectively, as a result of residual stress relaxation and in-situ over-aging.

Shear band formation and wear mechanism of titanium alloy powder metallurgy material prepared by HIP using Ti-6Al-4V pre-alloy powder

In this paper, wear mechanism model and shear plane formation model were built based on the influence of residual micro-void of powder metallurgy material on chip-tool interaction and serrated chip shear plane. In the wear mechanism model, the micro-void in the chip back surface tore and accumulated adhered workpiece material in sticking and sliding zones, respectively. In the occasional random shear model, the micro-void increased the change rate of the speed component near the micro-void to cause the shear plane shifts to the micro-void. Ti-6Al-4V powder metallurgy material was prepared with hot isostatic pressing technology to carry out machining experiment. The wear mechanism model and the occasional random shear model were verified with the research on micro-fluctuation of cutting force, wear morphology of cutting tool, and cross section of serrated chip.

Industrial Sintering Response and Microstructural Characterization of Aluminum Powder Metallurgy Alloy Alumix 123

In this work, the industrial sintering response of the commercial aluminum powder metallurgy alloy ‘Alumix 123’ has been examined and the resulting microstructure investigated by optical microscopy, scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. Alumix 123 is similar in composition to wrought aluminum alloy 2014 and was revealed to develop a sintered density of 92% of theoretical using standard practices for industrial sintering. Microstructural investigations proved that as a result of industrial sintering, a number of embrittling iron-containing intermetallics are developed in addition to the desirable copper-rich intermetallics. To improve the density of sintered components, procedures were developed for secondary processing by ‘sizing’ (repressing) in a laboratory setting. The results showed that sizing to the industry standard reduction in height of 5% only closed a portion of open surface porosity and that higher sizing pressures should be used in applications that are sensitive to this microstructural feature.

Effects of Sintering Temperature and Time on the Properties of Al-Cu PM Alloy

Abstract Aluminium-based powder metallurgy (PM) alloys have a number of advantages over cast and wrought aluminium alloys. These PM alloys can be produced using either prealloyed or elemental premixes, with the latter offering a longer die life because of their softer nature compared with prealloyed powders. It is found that the use of an Al-Cu premixed PM alloy gives green density values higher than those of Al-Cu prealloyed systems reported in the literature. Most commercial aluminium PM alloys and alloy developments are based on the Al4Cu system. The amount of liquid phase has significant effects on the microstructure and the mechanical properties of sintered products. Lack of a liquid phase results in inadequate mechanical properties, while an excess of liquid phase causes distortion and shape deformation of the compacts formed by sintering. The objective of this study is to determine the properties of an Al4Cu PM alloy produced using an elemental premix. The effects of the amount of liquid phase on microstructural features and mechanical properties are assessed through thermal analyses. It is found that the optimum transverse rupture strength is obtained by sintering at 600 °C for 2 h.

Experimental Investigations on Plastic Deformation and Densification Characteristics of P/M Fe–C–Cu–Mo Alloy Steels Under Cold Upsetting

Powder metallurgy (P/M) alloy steel containing copper (Cu) and molybdenum (Mo) has tremendous potential in various industrial sectors. The present work investigates the effects of Cu and Mo addition on plastic deformation/densification characteristics of P/M plain carbon (Fe–0.5%C) steel. Sintered preforms of 1 and 2% addition of Mo and Cu to the plain carbon steel were subjected to cold upsetting by applying uni-axial load on the preforms. The compressive stress was gradually applied and increased on the alloy steel preforms till fine crack appears on lateral surface of the deformed preforms. Various analytical stresses useful for die design are evaluated using conventional plasticity correlations. The plain carbon steel is observed to exhibit better densification and deformation properties and higher strain hardening exponent value compared to other alloy steels. The basic ferrite–pearlite microstructure coupled with the presence of pore-free copper and Mo particulates is understood to influence the deformation and densification of Cu- and Mo-added alloy steels, respectively. The Cu- and Mo-added alloy steels require more axial compressive stress to attain same level of plastic deformation and densification of the plain carbon steel. Addition of Cu and Mo to the plain steel is observed to reduce the plastic flow and densification level during cold upsetting.

Thermal stability and microstructure development of cast and powder metallurgy produced Mg–Y–Zn alloy during heat treatment

Abstract Response to isochronal annealing up to 440 °C of squeeze cast Mg–Y–Zn alloy and of the same alloy prepared by powder metallurgy (PM) and extruded at 280 °C was studied by resistivity and microhardness measurement, differential scanning calorimetry (DSC) and microstructure investigation. Electrical resistivity was measured at 77 K and microhardness was measured at room temperature after each annealing step. DSC measurement was performed at various heating rates. Transmission and scanning electron microscopy and optical microscopy revealed ribbons of long-period ordered structure (LPSO) 18R and planar defects within grain boundaries. Relatively high density of planar defects was found in grain interiors of the cast alloy with the grain size approximately 50 µm. Well pronounced subgrains were observed in the PM prepared alloy. Secondary phase particles decorate grain boundaries in this alloy. Three precipitation processes were detected in the cast alloy during repeated isochronal annealing up to 440 °C, whereas only one significant process was revealed in the PM alloy. These processes were identified as embedding of stacking faults by solutes, development and rearrangement (18R → 14H) of LPSO phase and development of grain boundary particles. A coarsening of grain boundary particles rich in Y and Zn only proceeds in the PM alloy. Activation energies of the precipitation processes were determined. Microhardness exhibits good thermal stability against annealing up to 360 °C in the PM alloy.

Isothermal Oxidation Comparison of Three Ni-Based Superalloys

Ni-based superalloys are used for high-temperature components of gas turbines in both industrial and aerospace applications due to their ability to maintain dimensional stability under conditions of high stress and strain. The oxidation resistance of these alloys often dictates their service lifetime. This study focuses on the isothermal oxidation behavior of three Ni-based superalloys, namely, polycrystalline cast IN738LC, single-crystal N5, and a ternary Ni-Fe-Cr (TAS) powder metallurgy alloy. The isothermal oxidation tests were conducted at 900 °C in the static air up to 1000 h, and the specific aspects studied were the oxidation behavior of these chromia-forming and alumina-forming alloys that are used extensively in industry. In particular, the behavior of oxide scale growth and subsurface changes were analyzed in detail using various techniques such as SEM, EDS, and AFM. From the isothermal oxidation kinetics, the oxidation rate constant, k p, was calculated for each alloy and found to be; k p = 2.79 × 10−6 mg2 cm−4 s−1 for IN738LC, k p = 1.42 × 10−7 mg2 cm−4 s−1 for N5 and k p = 1.62 × 10−7 mg2 cm−4 s−1 for TAS. Based on a microstructural analysis, IN738LC exhibited a continuous dense outer scale of Cr2O3 and discontinuous inner scale of Al2O3, whereas N5 and TAS showed a dense outer scale of Al2O3 alone. The results suggested that the N5 and PM-TAS alloys are more oxidation resistant than the IN738LC under these conditions.

Image Analysis Software for Porosity Measurements in Some Powder Metallurgy Alloys

The present research was aimed to study the porosity in some powder metallurgy (P/M) alloys using an image analysis software. The porosity in P/M parts is an important parameter because is affecting the mechanical properties. Also, porosity is in correlation with processing parameters such as green density, alloying elements, particle size. The conventional method for porosity measurements of powder metallurgy products is using the density technique. Another method for porosity measurements was using an image processing software and by applying filters and adjustments the detection of the pores (black areas) was done. Two types of powders obtained by water amotization were subjected to analyze. To obtain the green compacts, the powders were pressed at 600 MPa using a single die action. The green compacts were sintered in a laboratory furnace at 1150o C for 30 and 120 minutes. A metallographic analysis was performed for porosity measurements. The pore’s shape and porosity fraction were measured using both conventional and image analysis techniques. The porosity measurements for sitnered specimens obtained from image analysis was slightly higher than that from density technique.

Defocusing Effects of Laser Beam on the Weldability of Powder Metallurgy Ti-Based Shape Memory Alloys

The influence of defocusing distance of the fiber laser welding on Ti-51at%Ni, Ti-28%atNb and Ti-30at%Ta shape memory alloys (SMAs) was investigated. These alloys were produced by powder metallurgy (P/M) and sintered by furnace and microwave processes. The experimental results showed that the furnace-sintered Ti-Ni welds have the maximum porosity density and the lowest weld quality. While, the microwave sintered alloys of Ti-Nb and Ti-Ta SMAs presented better weldability, even though porosities were still observed. Ti-Ta SMA showed the best welding quality compared with the other welded joints. It can be concluded that porosities play important role in the welding of powder metallurgy alloys and in order to achieve high-quality welds, the porosities should be minimized.

Surface microstructure and properties of Cu-C powder metallurgical alloy induced by high-current pulsed electron beam

This paper investigates the microstructure and properties of Cu-6C powder metallurgy (PM) alloys irradiated by high-current pulse electron beam (HCPEB). After 20-pulsed HCPEB irradiation, the surface was melted completely and the remelted layer was formed in 2–3 μm thickness, which consisting of ultrafine Cu grains. Within the near irradiated surface, high-density dislocations and vacancy clusters were observed which provide a large amount of paths for carbon atoms to diffuse into Cu matrix, and it leads to the formation of the supersaturated solid solution, causing Cu lattice parameter expansion. In addition, the extreme rapid cycle generated the ultrafine carbon particles at the surface of Cu-6C metallic matrix. The results of microhardness measurements and sliding wear resistance testing indicated that the irradiated sample exhibited better properties than the initial one. The ultrafine carbon particles played an important role in the antifriction properties, which was attributed to the formation of carbonic tribolayer on the hard surface.

Application of Recycled Tungsten Carbide Powder for Fabrication of Iron Based Powder Metallurgy Alloy

Application of Recycled Tungsten Carbide Powder for Fabrication of Iron Based Powder Metallurgy Alloy

Sintering and aging behaviours of Al4CuXMg PM alloy

Sintering and aging behaviours of Al–Cu–Mg powder metallurgy (PM) alloy produced from elemental powders were examined. After evaluating results from thermal analysis, tests were carried out on Al–4Cu alloys with magnesium contents of 0.5, 1 and 2 wt-% and it was found that additions of 1 wt-% Mg was most effective for enhancing the transverse rupture strength (TRS) of the Al–Cu PM alloys for both as sintered and after a heat-treatment conditions. Grain size reduction in the range of 14–45% was achieved by adding magnesium into Al–Cu system. Analyses showed that produced alloys were composed of Al, Al2Cu, Al2CuMg and Al7Cu2Fe phases. Differential scanning calorimeter and dilatometer analyses revealed that alloys show swelling behaviour after the eutectic melting reaction at 548°C and swelling rates increasing as a function of magnesium content. Both high hardness value (120 HB) and TRS (650 MPa) were achieved via aging of Al4Cu1Mg alloy for 24 hours.

Porcelain bonding to novel Co–Cr alloys: Influence of interfacial reactions on phase stability, plasticity and adhesion

ObjectiveThe objective of the present study was to determine the hardness and adhesion strength at the porcelain to alloy interface. Methods15 bi-layer porcelain veneered Co–Cr specimens of each alloy group [cast, powder metallurgy (PM), CAD/CAM(CC)] were manufactured. 12 bi-layered specimens were tested using four-point bend strain energy release rate adhesion test. One before and after porcelain firing specimen of each alloy group were nano-indented at the bulk and metal-porcelain interface to determine the mechanical properties. Electron backscatter diffraction was used to determine the microstructure and phase of the indented areas. ResultsThe results obtained from the four-point bend strain energy release rate test indicated highest adhesion energy of 92.15J/m2 observed in the CC produced Co–Cr alloy. This was followed by the PM alloy with an adhesion energy of 62.24J/m2 and cast alloy with an adhesion energy of 42.83J/m2. All comparisons of adhesion energy between the three alloys were found to be statistically significant (p<.05). Nano-indentation test indicated higher hardness values of 4.6–6.1GPa at the metal-porcelain interface compared to the bulk, which had hardness values of 3.1–3.9GPa. SignificanceThe adhesion of the alloy to porcelain was found to be inversely related to the hardness of the interfacial layer at the alloy surface. Lower interfacial hardness was found to be accompanied with higher adhesion energy due to the additional plastic energy consumed during crack propagation along the more ductile interface region of the alloy.

Effect of Process Variables on the Inertia Friction Welding of Superalloys LSHR and Mar-M247

The effect of inertia friction welding process parameters on microstructure evolution, weld plane quality, and the tensile behavior of welds between dissimilar nickel-base superalloys was established. For this purpose, the fine-grain, powder metallurgy alloy LSHR was joined to coarse-grain cast Mar-M247 using a fixed level of initial kinetic energy, but different combinations of the flywheel moment of inertia and initial rotation speed. It was found that welds made with the largest moment of inertia resulted in a sound bond with the best microstructure and room-temperature tensile strength equal to or greater than that of the parent materials. A relationship between the moment of inertia and weld process efficiency was established. The post-weld tensile behavior was interpreted in the context of observed microstructure gradients and weld-line defects.